Measurement module of virtual vector network analyzer

ABSTRACT

A hand-carriable, single port measurement module of a virtual vector network analyzer is sized and configured so as to be directly connectable to devices typically located within confined spaces normally requiring the use of an intervening test cable and which may be closely spaced to other devices that may need to be tested by other measurement modules. The measurement module includes a single test port extending from a housing wherein the housing is elongated along the axis of insertion of the test port and has a length substantially less than 12 inches. A circuit disposed within the housing is configured to transmit and receive test signals through the test port for measurement of a device under test and to transmit digitized signals representing the test signals through a communication interface of the module to a user interface separate from the housing for presentation to a user.

RELATED APPLICATION DATA

This application is a continuation of U.S. application Ser. No.13/591,124 filed Aug. 21, 2012, now U.S. Pat. No. 9,291,657, thecontents of which are incorporated by reference.

BACKGROUND

Embodiments relate to vector network analyzers and, in particular,hand-held virtual vector network analyzer measurement modules.

Current vector network analyzers (VNA) exist in either desktop orportable implementations. Desktop VNAs can have built-in user interfacesincluding displays, keyboards, or the like. The large size of thesedevices, even in the portable implementation, makes it difficult orimpossible to perform measurements immediately on the connectors of thedevices-under-test (DUTs) without the use of RF test cables.

In addition, even with precision test cables, a DUT may be located in arelatively confined location such that the VNA cannot be calibrated withthe test cables in their final positions, potentially introducing errorsinto the measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a vector network analyzer according to anembodiment.

FIGS. 2-4 illustrate a vector network analyzer measurement moduleaccording to another embodiment.

FIG. 5 illustrates a test cable attached to a device-under-test in anenclosure.

FIG. 6 illustrates a vector network analyzer attached to adevice-under-test in an enclosure according to an embodiment.

FIG. 7 is a block diagram of a vector network analyzer measurementmodule according to an embodiment.

FIG. 8 is a block diagram of a vector network analyzer measurementmodule according to another embodiment.

FIG. 9 is a diagram of a vector network analyzer according to anotherembodiment.

DETAILED DESCRIPTION

In an embodiment, a virtual vector network analyzer measurement module'sportability, virtual format, and power draw from a computer interfaceallows a user to conduct tests directly linking the analyzer test portsand a DUT. The resulting benefit is a considerable enhancement inaccuracy; meanwhile, the vector network analyzer (VNA) operation becomeseasier and more cost-effective.

FIG. 1 is a diagram of a VNA according to an embodiment. In thisembodiment, a VNA 1 includes a portable measurement module 6 coupled toa computer 2 by a cable 4. The measurement module 6 is configured togenerate and receive test signals. The measurement module 6 includeshigher-frequency components, such as oscillators, synthesizers,couplers, splitters, bridges, mixers, amplifiers, filters, transmissionlines, or the like. These components are configured to generate andmeasure test signals of the incident wave for transmission out of a testport of measurement module 6 to the DUT and receive test signals of thereflected wave from the DUT through the aforementioned port. As will bedescribed in further detail below, other components of measurementmodule 6 process the test signals into a format suitable fortransmission over cable 4 to personal computer 2.

For example, a synthesizer in the measurement module 6 generates asingle frequency incident test signal. That test signal is mixed with alocal oscillator signal generated by a second synthesizer, and togetherthey form the IF signal corresponding to the test signal of the incidentwave. The incident test signal is also transmitted out of a test port ofthe measurement module 6. The measurement module 6 receives the incidenttest signal, reflected off of a DUT, if present, as a reflected testsignal. The reflected test signal is mixed with the local oscillatorsignal, and together they form the IF signal corresponding to the testsignal of the reflected wave. These IF incident and reflected testsignals are digitized in the measurement module 6. The measurementmodule 6 is configured to generate a phasor representation of a ratio ofthe IF incident and reflected test signals. The phasor representationfor one or more test signal frequencies are digitized test signals thatare transmitted to the computer 2 over the cable 4. Accordingly, aposition, movement, deterioration, or the like of components between themeasurement module 6 and the computer 2 will not have any effect on themeasurement accuracy.

The cable 4 is associated with a power and communication interface. Inthis embodiment, the cable 4 is a universal serial bus (USB) cable. Acorresponding USB port of the computer 2 provides both communicationsand power to the measurement module 6.

The digitized signals are transmitted to the computer 2 through thecable 4. Accordingly, the user interface of the VNA 1, such as adisplay, keyboard, buttons, knobs, other processing circuitry, or thelike, is separate from a housing including a test port of themeasurement module 6. As a result, the measurement module 6 is smallerthan a conventional device integrated with the user interface.

The computer 2 is configured to present a user interface formanipulating the magnitude and phase signals and/or any derivedinformation. For example, the computer 2 is configured to present adisplay of phase, magnitude, delay, or the like of the received signalsin response to user input. The computer 2 is configured to present theinformation in Cartesian graphs, Smith charts, or the like.

Since the user interface is located at the computer 2, user interfacecomponents are not present at the measurement module 6, thus reducing asize and power consumption of the measurement module 6. The smaller sizeallows the measurement module 6 to be directly connected to a deviceunder test (DUT). That is, no test cables are needed. In contrast, ifthe measurement module 6 was integrated with the user interface, testcables would be required to couple to a DUT.

By eliminating the need for a test cable, any variation in measurementdue to the test cables, such as variations due to environmental changes,movement of the test setup, or the like is eliminated. For example, whenthe VNA 1 is calibrated, the calibration is performed at the test portmounted to the measurement module 6. Since any circuitry, cables,transmission lines, or the like between the connector of the measurementmodule 6 and any sensing circuitry is contained within a housing of themeasurement module 6, movement of the measurement module 6 will have asubstantially reduced, if not negligible effect on the calibration ofthe VNA 1.

The cable 4 allows for flexibility in positioning the measurement module6 that both accommodates positions available by using a test cable andpositions prohibited by a test cable. For example, a DUT is located in aphysically constrained location, such as within a cabinet, a vehiclechassis, or the like. Routing and manipulation of the cable 4 whenattaching the measurement module 6 does not substantially affect acalibration of the VNA 1 since the interface cable 4 need not be aprecision test cable. Accordingly, costs to locate the test port of theVNA 1 at a desired location are reduced.

Although a computer 2 has been given as an example, other types ofdevices can be used. For example, a laptop computer, desktop computer,test and measurement instrument, tablet computer, smartphone, or thelike can be used. Any device with a suitable communication interfacethrough which power is provided may be used.

Although a USB cable has been given as an example of the cable 4, othercables and interface systems can be used to enable communication andsupply power. In another embodiment, the computer 2 is configured toprovide a power-over-Ethernet connection. The power and communicationinterface is any communication interface that supplies power, whetherthrough separate connections of the cable 4 or multiplexed with thecommunication signals.

FIGS. 2-4 illustrate a vector network analyzer measurement module 10according to another embodiment. The measurement module 10 includes ahousing 12 with a test port 14 mounted on the housing. A power andcommunication interface 22 is disposed opposite the test port 14. Inanother embodiment, the interface 22 is disposed in other locationswhere the interface 22 and any connecting cable do not interfere withthe test port 14 and mounting the test port 14 to a DUT.

The housing 12 defines a first dimension 20 that is preferably less thanabout 2 inches. In an embodiment, the first dimension is less than about1 inch. The housing 12 has a second dimension 24 that is preferably lessthan about 1.5 inches. In the illustrated embodiment, the firstdimension 20 and second dimension 24 are the smallest major dimensionsof the housing 12.

The dimensions 20 and 24 are dimensions of the measurement module 10allow a user to grip the measurement module 10 substantially within theuser's hand. In an embodiment, the length of a perimeter substantiallyformed by dimensions 20 and 24 is less than about 12 inches, andpreferably less than about 5 inches.

In an embodiment, dimensions 20 and 24 are substantially perpendicularwith the insertion axis defined by the test port 14. Accordingly, across-section of the housing 12 is smaller, allowing the measurementmodule to be attached to a DUT within a confined space. When DUTs areclosely spaced, movement in a plane substantially perpendicular with aninsertion axis of a port of the DUT is limited. Accordingly, the reducedcross-sectional size of the housing allows the measurement module 10 tobe directly connected to a DUT in such an environment.

In an embodiment, a third dimension 18 of the housing is less than about5 inches. Accordingly, the housing 12 fits comfortably in a user's hand.When a user holds the housing 12 in one hand, the user attaches the testport 14 to a DUT using the other hand, for example, with an appropriatetorque wrench. The dimensions described above result from separating theuser interface device from high frequency circuitry within themeasurement module 10.

FIG. 5 illustrates a test cable attached to a device-under-test in anenclosure. In an embodiment, a DUT 42 is mounted in an enclosure 40. Theenclosure 40 has a surface 41, such as a wall, shelf, panel, or thelike, that least partially obstruct access to a connector 44 of the DUT42.

As illustrated, a test cable 46 with connector 48 is coupled to theconnector 44 of the DUT 42. Test cables 46 have a specified minimum bendradius below which performance of the cable 46 is undefined.Accordingly, when coupling the test cable 46 to the DUT 42, the bendradius 50 may approach the test cable's 46 minimum bend radius due tothe confines of the space.

In addition, a calibration must be performed at the connector 48 tosubstantially eliminate effects of the cable. However, it is impracticalto calibrate the VNA at the connector 48 inside of the enclosure 40,particularly with the cable 46 in substantially the same position aswhen coupled to the DUT 42. Thus, the calibration must be performedoutside of the enclosure 40. As a result, the test cable 46 will nothave the same physical characteristics such as position, bend radius, orthe like between when the VNA is calibrated and when the test cable 46is coupled to the DUT 42. Thus, errors in measurements are introduced.

FIG. 6 illustrates a vector network analyzer attached to adevice-under-test in an enclosure according to an embodiment. In thisembodiment, a measurement module 60 is directly coupled to the DUT 42.Connector 62 of the measurement module 60 is directly connected to theconnector 44 of the DUT 42.

In this embodiment, a dimension 66 of the housing of the measurementmodule 60 along an axis of insertion of the DUT connector 44 is lessthan a minimum bend radius of cable operable over a frequency rangeincluding a frequency range of the vector network analyzer. That is, theposition of the DUT 42 accommodates a test cable with a bend approachingthe minimum bend radius. Since the size of the measurement module 60 issmaller than the minimum bend radius, the measurement module can beinserted into the same space and coupled to the DUT 42.

Moreover, the measurement module 60 is calibrated outside of theenclosure 40. In contrast to the test cable 46, moving the measurementmodule 60 into the enclosure 40 will not substantially change theconditions under which the measurement module 60 was calibrated. Thatis, the calibration was performed at the connector 62. The connector 62is substantially rigidly mounted to the housing of the measurementmodule 60. Thus, substantially no relative motion will occur between thecalibrated port and the sensing circuitry. Any movement, change inposition, or the like of cable 64 will not affect the calibration sinceonly digitized signals are transmitted over the cable 64.

In an embodiment, locating the user interface external to the housing 12results in a measurement module 10 that is lighter than a conventionalVNA. The absence of components like the display, power supply, keyboard,and the housing necessary for their containment, eliminates additionalweight to the measurement module 10. In an embodiment, theVNA-measurement module 10 weighs less than about 250 g.

FIG. 7 is a block diagram of a vector network analyzer measurementmodule according to an embodiment. In this embodiment, the measurementmodule 80 includes a housing 82. A power and communication interface 84and a test port 86 are mounted on the housing. The measurement module 80also includes a controller 88 and microwave electronics 90.

The microwave electronics 90 are configured to generate an incidentsignal to transmit through the test port 86 and receive a reflectedsignal through the test port 86. The microwave electronics 90 includesynthesizers, mixers, couplers, splitters, resistive bridges, or thelike for generating and processing incident test signals and receivedtest signals, whether reflected off of another device or transmittedfrom another measurement module. In an embodiment, the microwaveelectronics 90 include the circuitry to generate test signals andconvert both transmitted and received test signals into lower frequencyintermediate frequency (IF) signals and/or phasor representations. Thatis, high frequency circuitry and connections for signals needing asignal path that is affected by geometry, position, motion, or the likeis contained within the measurement module 82.

The controller 88 is configured to receive such IF signals or similarsignals and generate digitized signals for transmission through thepower and communication interface 84. In an embodiment, the controller88 includes a general purpose processor, an application specificintegrated circuit, a digital signal processor, a programmable logicdevice, a combination of such circuits, or the like. In an embodimentthe controller 88 includes integrated analog to digital converters, dataports for external analog to digital converters, or the like. Inaddition, the controller 88 includes integrated communication interfacessuch as USB ports, Ethernet ports, external implementations of suchports, or the like.

The measurement module 80 is configured to obtain power from the powerand communication interface 84. That is, the power for the controller 88and microwave electronics 90 is obtained through the power andcommunication interface. In this embodiment, no other power supply ispresent.

FIG. 8 is a block diagram of a vector network analyzer measurementmodule according to another embodiment. The measurement module 110includes a test port 116 and a power and communication interface 114mounted on a housing 112 similar to a measurement module describedabove. In this embodiment, the measurement module 110 includes a firstsynthesizer 128 and a second synthesizer 122.

The first synthesizer 128 is formed in an integrated circuit 120. Thefirst synthesizer 128 includes one or more oscillators, frequencydividers, frequency multipliers, attenuators, amplifiers, filters, orthe like to generate a desired signal. In particular, the firstsynthesizer 128 is used to generate an incident signal for themeasurement module 110.

The first synthesizer 128 is coupled to the controller 152. Thecontroller 152 is configured to set various parameters of the incidentsignal, such as frequency power, dividing/multiplying ratio, or thelike.

The incident signal is provided to a resistive bridge or splitter 132.In an embodiment a resistive bridge couples the incident signal to theresistive bridge 136 and a mixer 126. Accordingly, the incident signalis transmitted out of the test port 116 and downconverted through themixer 126 for measurement.

The measurement module 110 includes a second synthesizer 122. The secondsynthesizer 122 is formed in an integrated circuit 118. The secondsynthesizer 122 includes one or more oscillators, frequency dividers,frequency multipliers, attenuators, amplifiers, filters, or the like togenerate a desired signal. In addition, the integrated circuit 118including the second synthesizer 122 includes mixers 124 and 126. Inparticular, the second synthesizer 122 is configured to generate a localoscillator signal for mixers 124 and 126.

The second synthesizer 122 is coupled to the controller 152. Thecontroller 152 is configured to set various parameters of the incidentsignal, such as frequency power, dividing/multiplying ratio, or thelike. Accordingly, the controller 152 is configured to set parameters ofthe incident signal from the first synthesizer 128 and the localoscillator signal from the second synthesizer 122 such that the incidentsignal and a reflected signal are downconverted to a desired IF signalfrequency range. That is, the incident signal is downconverted in themixer 126 and the reflected signal received through the test port 116 iscoupled to the mixer 124 through the resistive bridge 136 anddownconverted to the desired IF signal frequency range. The controller152 is configured to sweep frequencies of the first synthesizer and thesecond synthesizer and substantially maintain a frequency offset betweenthe incident signal and the local oscillator signal. In anotherembodiment, the controller 152 is configured to receive commands throughthe power and communication interface 114 to control a sweep of testsignals.

Although a splitter and resistive bridge have been used as examples, inan embodiment, other components and structures are used to isolatesignals. For example, circulators, couplers, a combination of suchcomponents, or the like are used to route the incident and reflectedsignals.

In an embodiment, an IF incident signal 146 and an IF reflected signal148 are digitized in digitizers 150. The controller 152 is configured tofurther process the digitized signals 156 and 158 for storage in thememory 154, transmission through the power and communication interface114, or the like. In an embodiment, the controller 152 is configured toconvert the IF signals into a phasor representation of the reflectedsignal using the incident signal as a reference. Coefficients from acalibration are applied by the controller 152 or at a later time aftertransmission. In another example, the digitized IF signals aretransmitted through the power and communication interface 114. A userinterface is configured to apply a correction for a calibration. Thatis, once the high frequency signals are converted into lower frequencyand/or digital signals, any amount of processing of the signals aredistributed between the measurement module 110 and a user interface fromcomplete processing of the signals at the user interface to completeprocessing of the signals at the measurement module. However, thepresentation of any resulting measurements occurs at the user interface,separate from the measurement module.

In an embodiment, the digitizers 150 are integrated with the controller152. For example, a microcontroller, application specific integratedcircuit, or the like includes integrated analog to digital converters.In addition, at least a part of the power and communication interface114 is included in the controller. In an embodiment, the controller 152includes a communication portion of a USB interface. Accordingly, size,weight, power consumption, or the like is reduced by using suchintegrated components described above.

In an embodiment, the memory 154 is any variety of memory. For example,the memory 154 includes static memory, dynamic memory, flash memory, anelectrically erasable programmable read only memory (EEPROM), acombination of such memories, or the like. In an embodiment. the memory154 is configured to store factory correction coefficients, usercalibration coefficients and the software for installation onto anexternal user interface to control the measurement module 110. In anembodiment, the memory 154 is separate from the controller 152,integrated with the controller 152, a combination of external andinternal memory, or the like.

Although a single synthesizer 128 has been described for generating anincident signal, in an embodiment, multiple synthesizers, oscillators,or the like are present. For example, an additional synthesizer ispresent to increase the measurement range of the measurement module.Additional test signal amplifiers, frequency multipliers, frequencydividers, attenuators, filters, switches, or the like are present.

In an embodiment, the measurement module 110 includes a referencefrequency generator, a programmable automatic frequency control, areference frequency input, or the like. The synthesizers 122 and 128 areconfigured to be phase locked to such a reference frequency signal.

In an embodiment, a measurement range of the measurement module 128 isextended. The mixers 124 and 126 are driven with a local oscillatorsignal having a frequency that is one third of a sum or difference of afrequency of the incident signal and an intermediate frequency signal. Athird harmonic of such a local oscillator signal, generated in themixer, downconverts the higher frequency incident signal. Accordingly,smaller, lower frequency components are used for a higher operatingfrequency range. As a result, the size, weight, power consumption, orthe like of the measurement module 110 can be reduced.

In an embodiment, integrating the higher frequency components allows fora smaller footprint, yet a higher frequency range. For example, with theintegrated circuits 118 and 120 described above, the frequency range ofthe measurement module can be extended up to about 5 GHz or greater, forexample up to at least 5.4 GHz. In another example, the upper frequencylimit can be about 13 GHz or greater, for example, at least about 13.5GHz.

FIG. 9 is a block diagram of a vector network analyzer according toanother embodiment. As described above, the measurement module 6 is usedas a vector reflectometer. That is, measurement module 6 is used as partof a single port vector network analyzer. In another embodiment,multiple measurement modules are used to create a multi-port VNA.

In this embodiment, a VNA 170 is configured similar to the VNA 1 ofFIG. 1. However, an additional measurement module 174 is coupled to thecomputer 2 with a cable 172 similar to the cable 4. Accordingly, testsignals are generated from either measurement modules 6 and 174. Usingthe measurement module 6 as an example for generating an incidentsignal, the incident signal is transmitted through a DUT (not shown) tothe measurement module 174.

Accordingly, the measurement module 174 measures the transmitted,incident signal. For example, the measurement module 174 measures amagnitude of the transmitted incident signal. That is, the measurementmodule 174 operates as a scalar test analyzer.

In another example, the measurement module 174 is configured to receivethe transmitted incident signal and generate an internal referencesignal. For example, a reference signal, such as a 10 MHz referencesignal, can be used to synchronize the measurement modules 6 and 174 tophase lock the internal reference signal to the incident signal.Accordingly, a phase locked local oscillator signal within themeasurement module 174 is generated to downconvert a received incidentsignal to an IF frequency range. In another example, the synchronizationcan be implemented with a programmable automatic frequency control.

In an embodiment, the user interface is provided by the computer 2.Accordingly, the VNA 170 operates as a conventional two-port VNA, albeitwithout various constraints as described above. However, the computer 2need not be the interface for the measurement modules. In an embodiment,in a manufacturing setup, a test instrument has several measurementmodules. Each of the measurement modules operate substantiallyindependently as reflectometers, or in conjunction as multi-port testsetups. To transition from a single-port or two-port setup to amulti-port setup of multiple single or two port setups, a user need onlyacquire additional measurement modules, rather than purchasing an entirenew instrument or an entire new multi-port test set.

In an embodiment, multiple reflectometers, two-port setups, andmulti-port setups, are coupled to the same user interface. In anembodiment, a computer has multiple USB ports, each of which is coupledto a USB hub with multiple ports. Each terminal USB port is coupled toan associated measurement module. Although a USB hub has been used as anexample, any switch, router, computer, or other communication device isused to distribute measurement modules in desired location.

Although particular embodiments have been described above, the scope ofthe following claims is not limited to these embodiments. Variousmodifications, changes, combinations, substitution of equivalents, orthe like is made within the scope of the following claims.

The invention claimed is:
 1. A hand-carriable, single port measurementmodule of a virtual vector network analyzer that is sized and configuredso as to be directly connectable to devices typically located withinconfined spaces normally requiring the use of an intervening test cableand which are closely spaced to other devices that need to be tested byother measurement modules, wherein the measurement module comprises: asingle test port extending from one end of an elongated housing, thehousing containing a circuit that is configured to: transmit and receivetest signals through the test port for measurement of a device undertest; and transmit digitized signals representing the test signalsthrough a communication interface of the measurement module to a userinterface that is separate from the housing for presentation to a user;wherein the housing defines a first dimension along an axis of insertionof the test port and second and third dimensions that are eachtransverse to the axis of insertion; wherein the first dimension issubstantially less than 12 inches; wherein the second and thirddimensions are each substantially less than the first dimension; andwherein the length of a perimeter of the housing substantially formed bythe second and third dimensions is substantially less than 12 inches;whereby the dimensions of the housing allow the measurement module tofit comfortably in a user's hand and be directly connected to a typicaldevice under test without the need for an intervening test cable.
 2. Themeasurement module of claim 1 wherein the first dimension is less than 6inches.
 3. The measurement module of claim 1 wherein the first dimensionis about 5 inches.
 4. The measurement module of claim 1 wherein at leastone of the second and third dimensions is about 2 inches or less.
 5. Themeasurement module of claim 4 wherein the second and third dimensionsare each about 2 inches or less.
 6. The measurement module of claim 4wherein the length of the perimeter substantially formed by the secondand third dimensions is less than 8 inches.
 7. The measurement module ofclaim 1 wherein the communication interface is mounted to an end of thehousing that is opposite the test port.
 8. The measurement module ofclaim 7 wherein the communication interface comprises a power andcommunication interface.
 9. The measurement module of claim 1 whereinthe circuit is configured to: generate a local oscillator signal;generate a digitized incident wave intermediate frequency signal inresponse to a synthesized incident wave test signal and the localoscillator signal; generate a digitized reflected wave intermediatefrequency signal in response to a reflected signal received through thetest port and the local oscillator signal; generate a phasorrepresentation of a ratio of the digitized incident wave intermediatefrequency signal and the digitized reflected wave intermediate frequencysignal; and transmit the phasor representation as one of the digitizedsignals.
 10. The measurement module of claim 1 wherein the circuitcomprises: microwave electronics coupled to the test port; and acontroller configured to digitize signals from the microwave electronicsand transmit the digitized signals through the communications interface.11. The measurement module of claim 10 wherein the microwave electronicsfurther comprise: a first integrated circuit including a firstsynthesizer configured to generate an incident wave signal; and a secondintegrated circuit including a first mixer, a second mixer, and a secondsynthesizer configured to generate a local oscillator signal; wherein:the first mixer is configured to receive the incident wave signal andthe local oscillator signal; and the second mixer is configured receivea reflected wave signal from the test port and the local oscillatorsignal.
 12. The measurement module of claim 11 wherein the microwaveelectronics further comprise: a first resistor bridge configured toprovide the incident wave signal to the first mixer and the test port;and a second resistor bridge configured to provide the reflected wavesignal from the test port to the second mixer.
 13. The measurementmodule of claim 11 wherein the first mixer and the second mixer areconfigured to use a third harmonic of the local oscillator signal. 14.The measurement module of claim 1 wherein the communication interfacecomprises a universal serial bus interface.
 15. The measurement moduleof claim 1 further comprising a memory configured to store factorycorrection coefficients and user calibration coefficients.
 16. Themeasurement module of claim 1 in combination with a memory storingsoftware that, when installed on a computer external to the measurementmodule, causes the computer to present a user interface for the virtualvector network analyzer.
 17. A vector network analyzer comprising themeasurement module of claim 1 in combination with a user interface thatis separate from the housing of the measurement module and is configuredto receive the digitized signals representing the test signals from thecommunications interface of the measurement module.
 18. The vectornetwork analyzer of claim 17 wherein the user interface is configured totransmit control signals to the measurement module to control the testsignals transmitted by the measurement module.
 19. The measurementmodule of claim 1 wherein the first dimension is less than 6 inches, atleast one of the second and third dimensions is about 2 inches or less,and the communication interface comprises a universal serial businterface.
 20. The measurement module of claim 19 wherein themeasurement module draws its power through the universal serial businterface.